Generally, the Claus process is used to recover sulfur from hazardous waste gas streams containing hydrogen sulfide gas, such as various streams produced during refining of petroleum products, natural gas processing, and gasification. The Claus process entails partially combusting hydrogen sulfide to produce sulfur dioxide. Sulfur dioxide then reacts with the remaining hydrogen sulfide to produce sulfur. Sulfur is then recovered from the Claus process in a liquid form.
The liquid sulfur produced from the Claus process contains hydrogen polysulfides and dissolved hydrogen sulfide gas. The hydrogen polysulfides degrade slowly, producing toxic, odorous and highly flammable hydrogen sulfide gas. A large portion of the hydrogen sulfide gas is retained by the liquid sulfur as a dissolved gas. In untreated liquid sulfur, the hydrogen sulfide gas slowly diffuses into the vapor phase. The gradual degradation of the hydrogen polysulfides and the release of the dissolved hydrogen sulfide gas during storage and transportation involve substantial health, safety and environmental risks and may result in fire. For example, tests have shown that H2S concentrations of greater than 20 ppm by weight in liquid sulfur can result in closed vapor spaces having H2S concentrations greater than the lower explosion limit of 3.5%. Obviously, the explosivity concern is also coupled with the H2S toxicity concerns (H2S is toxic at 0.05%). Toxic levels of H2S can build up in closed vapor spaces of sulfur pits and transport containers. Also, high levels of H2S may accumulate near sulfur pits and sulfur loading areas.
Various processes have been developed to mitigate issues with the gradual release of hydrogen sulfide gas from liquid sulfur. For example, various sulfur degasification processes have been proposed to remove dissolved hydrogen sulfide (H2S) and hydrogen polysulfides (H2Sx) from the produced liquid sulfur, such as those disclosed in one or more of U.S. Pat. Nos. 4,131,437, 4,729,887, 4,844,720, 5,080,695, 5,632,967, 5,935,548, 6,149,887, 7,081,223, and 8,084,013, among others. Among these, processes are disclosed for bubbling air through liquid sulfur, as well as for co-current or counter-current contacting of air and liquid sulfur.
Common issues of these degasification processes are long residency times to achieve the desired hydrogen sulfide (H2S) level in the liquid sulfur, large plot space requirements for sulfur pit and associated degassing equipment, and corrosion of degassing vessels and/or internals located in or external of the sulfur pit and the associated maintenance of this equipment and/or these internals.